Multi-Channel Pulse Modulator System

ABSTRACT

The present invention relates to a multi-channel pulse modulator system comprising a pulse modulator circuit, wherein said pulse modulator circuit comprises an N-channel, wherein the modulator output is output from the pulse modulator circuit by means of L output connections of the pulse modulator circuit and where L is less than the number of modulator channels N. The invention further relates to a method of converting an N-channel pulse modulated signal into an M-channel signal, where M is less than N.

FIELD OF THE INVENTION

The invention relates to a multi-channel pulse modulator according tothe provisions of claim 1.

SUMMARY OF THE INVENTION

The present invention relates to a multi-channel pulse modulator systemcomprising a pulse modulator circuit PMC,

wherein said pulse modulator circuit PMC comprises an N-channelmodulator PWMS1, PWMS2, . . . PWMS6,

wherein the modulator output is output from the pulse modulator circuitPMC by means of L output connections OP1, OPL of the pulse modulatorcircuit PMC and where L is less than the number of modulator channels N.

According to the invention an advantageous interfacing has beenestablished between the modulator circuit and the switching stage in thesense that a multi-channel, e.g. N-channel signal, is modulated into anN or N set of parallel signals by the modular of the modulator circuitand the modulated signal may be encoded or converted into a signalrepresentation, which may be output from the modulator circuit in asmall-level signal by means of a number of output connections L, e.g. Loutput pins, which is less than the number of modulated channels. Inthis way, an advantageous export of modulated signals may be obtained bya reduced number of pins of the modulator circuit and by means ofsmall-level signals. L is at least one according to the invention. Thus,a complete multi-channel pulse, e.g. an N-channel modulated signal maybe transmitted as a one channel by e.g. ultimately one single outputconnection or e.g. as one channel by e.g. two output connections forminga differential output connection of the circuit. Numerous otherconfigurations of the output connection may be applied within the scopeof the invention.

This advantage is in particular advantageous in relation to a number ofmodulated small-level signal channels, which must be fed to a switchedhigh-level output stage.

When said multi-channel pulse modulation system further comprises aswitched output stage SWOS,

wherein said pulse modulator circuit PMC comprises an N-channelmodulator PWMS1, PWMS2, . . . PWMS6; PM,

wherein the modulator output is interfaced from the pulse modulatorcircuit PMC to the switching output stage SWOS by means of L outputconnections, e.g. output pins OP1, OPL, of the modulator circuit PMC andwhere L is less than the number of modulator channels N, an advantageousembodiment of the present invention is obtained.

When the L output connections (OP1, OPL) outputs an M-channel signalwhere M is less than N,

wherein said M-channel signal is established by a pulse signal combiner(PSC),

wherein said pulse signal combiner (PSC) combines at least one of saidM-channel signals into a non-coincident pulse modulated signal (202,203) representing at least a subset of an N-channel pulse modulatedsignal established by said N-channel modulator (PWMS1, PWMS2, . . .PWMS6; PM), an advantageous embodiment of the present invention isobtained.

When the number of output channels (OC1, OC2, OC3, . . . OCN) of theswitching output stage (SWOS) is N, an advantageous embodiment of thepresent invention is obtained.

When said pulse signal combiner (PSC) combines said N-channel pulsemodulated signal by an initial establishment of said N-channel pulsesignal of non-coincident pulses and whereby said non-coincident pulsessubsequently are combined into said M-channel signal, an advantageousembodiment of the present invention is obtained.

A very interesting feature of the signal combining and signal splittingaccording to the invention is that cross-talk in the multi-channeloutput stage may be minimized due to the fact that the pulsestransmitted over each of the M-channels by nature are non-coincident,thereby invoking that none of the output stages addressed by theM-channel switches at the same time unless a further signal processingoccurs during the signal splitting and distributing to the N-channels atthe receiving end.

When said M-channel output comprises a sequence of analog pulses, andwhereby said sequence of analog pulses defines the pulses of anN-channel pulse modulated signal, an advantageous embodiment of thepresent invention is obtained.

When said pulse modulator circuit comprises a pulse modulator chip(PMC), an advantageous embodiment of the present invention is obtained.

According to a preferred embodiment of the invention the pulse modulatorcircuit may comprise a single chip.

When said L connections comprises L output pins (OP1, OPL), anadvantageous embodiment of the present invention is obtained.

When said switched output stage (SWOS) is comprised in one single chip,an advantageous embodiment of the present invention is obtained.

The switched output stage may e.g. be comprised in one single chip,which may be advantageous in several different applications where amulti-channel amplifier is applied.

When said switched output stage (SWOS) is distributed in two or morechips, an advantageous embodiment of the present invention is obtained.

When applying a multi-chip or multi-components switched output stage anadvantageous embodiment may be obtained with respect to the singleswitching amplifiers and/or with respect to the arranging of theamplifiers in relation to space, cooling, topology in general, etc. Whenapplying two or more chips, a distribution method must be applied inorder to distribute the packed pulse modulated signal to the relevantchannel amplifiers of the output stage.

When said pulse modulation is a two-level modulation, a three-levelmodulation or a higher-level modulation, an advantageous embodiment ofthe present invention is obtained.

When said multi-channel pulse modulation system comprises a pulse widthmodulation system comprising a multi-channel pulse width modulatorcomprised in said pulse modulator circuit.

When said pulse modulation amplifier is an audio converter, anadvantageous embodiment of the present invention is obtained.

When at least one of said L-output connections (OP1, OPL) facilitate abidirectional communication between the modulation circuit (PMC) andsaid output stage, an advantageous embodiment of the present inventionis obtained.

A bi-directional communication established with respect to each outputor representation thereof facilitate that information may be fed backfrom the output stage to the pulse modulator circuit by means of fewconnections, e.g. pins. Such information may e.g. be the actualswitching times of the individual switched channels may be fed back tothe modulator circuit, thereby enabling e.g. a desired compensation ormodulation established responsive to actual switching times of theindividual output channels.

When said pulse modulator circuit (PMC) comprises at least oneconnection dedicated for receipt of information from the state of theoutput stage, an advantageous embodiment of the present invention isobtained.

When said output stage comprises a pulse signal splitter (PSS; 124), anadvantageous embodiment of the present invention is obtained.

When said pulse signal splitter (PSS; 124) corrects modificationsapplied in the pulse signal combiner (PSC), an advantageous embodimentof the present invention is obtained.

When correcting modifications applied to the N-channel pulse modulatedsignal in the pulse signal combiner, errors may be avoided in the finalpulse modulated signal of the relevant channel of the output stage.

It should of course be noted that such so-called errors may, accordingto a preferred embodiment of the invention, relate to deliberatemodifications of the N-channel pulse modulated signal in order to avoidsimultaneous switching of the channels of the output stage. Suchdeliberate errors should of course not be corrected.

When the number L of output connections is one, an advantageousembodiment of the present invention is obtained.

According to an embodiment of the invention, an M-channel signal may beoutput as a single-ended signal. Thus, according to an embodiment of theinvention, a one-channel signal may be transmitted by one outputconnection.

When the number L of output connections is two, an advantageousembodiment of the present invention is obtained.

According to an embodiment of the invention, an M-channel signal may beoutput as a differential signal.

When at least one of said M-channels are bidirectional, an advantageousembodiment of the present invention is obtained.

The advantage of applying bidirectionality between the pulse modulatorcircuit and the further switching circuitry is that e.g. switch delaytimes of the switching stage(s) may vary dynamically and may thereby beevaluated and compensated in the pulse modulator circuit. According toan embodiment of the invention, each of the applied M-channels aredirectional, thereby optimizing the signal flow between the pulsemodulator circuit and the switching stage.

When at least a subset of said M-channels are directed from the pulsemodulator circuit (PMC), an advantageous embodiment of the presentinvention is obtained.

When at least a further subset of said M-channels are directed to thepulse modulator circuit (PMC), an advantageous embodiment of the presentinvention is obtained.

An advantage of e.g. dedicating one or several channels as returnpath(s) is that a relatively exhaustive information about the actualswitching stage(s) and the general state of these stage(s) may be fed ona runtime basis back to the pulse modulator circuit for monitoring,evaluation and/or compensation purposes.

When said M-channel signal is converted into an N-channel signal anddistributed to N-channels of the output stage (AMP1, . . . , AMP6) aspulse modulated signals, an advantageous embodiment of the presentinvention is obtained.

When said N-channel signal distributed to said output stage correspondsto an N-channel signal established by an N-channel pulse modulator(N-PMS) of said pulse modulator circuit (PMC), an advantageousembodiment of the present invention is obtained.

The present invention further relates to a method of converting anN-channel pulse modulated signal into an M-channel signal, where M isless than N,

whereby said converting involves that at least one of said M-channelsignals are modified into a non-coincident pulse modulated signalrepresenting at least a subset of said N-channel pulse modulated signaland where said subset of said N-channel pulse modulated signal comprisesat least two channels.

When said converting of said N-channel pulse modulated signal involvesan initial establishment of said N-channel pulse signal ofnon-coincident pulses and whereby said non-coincident pulsessubsequently are combined into said M-channel signals, an advantageousembodiment of the present invention is obtained.

THE DRAWINGS

The invention will now be described with reference to drawings where

FIG. 1 illustrates principles of signal combining and signal splittingaccording to the invention in pulse modulator multi-channel systems,

FIG. 2 illustrates some general principles of the invention,

FIG. 3A-3C illustrate different properties of the individual channels ofthe modulator applied in the specific embodiment of FIGS. 4A and 4B,

FIG. 4A-4B illustrate specific multi-channel embodiments applying theprinciples of the present invention,

FIG. 5A-5B illustrate possible combination signals of the modulatoroutput signals according to an embodiment of the present invention, andwhere

FIG. 6 illustrates a more detailed view of a part of an embodiment ofthe present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates principles of signal combining and signal splittingapplied in an exemplary N-M-N pulse modulator multi-channel systemaccording to an embodiment of the invention.

According to the invention, an N-channel pulse modulated signal N-PMS,e.g. an N-channel pulse width modulated signal modulated according toconventional pulse width modulation principles is combined into anM-channel signal, preferably analog pulse modulated signal, by means ofa pulse signal combiner. The M-channel signal is interfaced from themodulator circuit by means of a number of L connections of the modulatorcircuit. The modulator may e.g. be comprised in a chip. According to theinvention, the number of output connections, e.g. output pins, of e.g. a6-channel modulator chip may be as low as one.

The M-channel signal may then be transmitted to an output stage andsplit into an N-channel pulse modulated signal by means of a pulsesignal splitter and thereby regenerated as intended and corresponding tothe principles applied when the N-channel pulse modulated signal wasestablished in the pulse modulator.

According to a very preferred embodiment of the invention, the N-channelpulse modulated signal should be established as a parallel sequence of Npulse modulated signal streams and where none of the switching times ofthe complete sequence or at least two of the N channels are coincident.Such a modulation technique facilitates low cross-talk in themulti-channel output stage and a relatively straightforward combining ofthe N-channels at the modulator side by the pulse signal combiner PSC asall pulses may be merged into one analog signal without conflictsarising from e.g. two coincident pulse trigger signals in two parallelN-channels.

FIG. 2 illustrates some general principles of the invention.

The illustrated pulse modulator system according to the inventioncomprises a pulse modulator circuit PMC receiving input signals IS. Theinput signals may have any form and be established internally in themodulator circuit PMC or they may be established by interfacing thepulse modulator circuit with another signal processing circuit. Inputsignals may comprise a single fast-running stream of data or a parallelstream of data, preferably one input line per channel.

The pulse modulator circuit may e.g. comprise a system of N pulsemodulator channels, e.g. six, where the input signal is converted into acorresponding number of streams of pulse modulation representations PMr.The pulse modulator combines the pulse modulation representations PMrinto a low number, e.g. one differential coding of all channels of thepulse modulation representations and interfaces the stream via L outputconnections OP1, . . . ,OPL, e.g. two, of the circuit PMC as an outputpulse modulation representation OPMr.

In this way, a multi-channel pulse modulation representation has beenestablished in a small-signal environment and represented as such, andthe multi-channel output pulse modulation representations OPMr have beeninterfaced with the environment by a number of modulator circuit PMCoutput connections OP1, . . . ,OPL which is lower than the number ofchannels N.

The output pulse modulation representations OPMr are then interfacedwith a multi-channel switched output stage SWOS by means of inputconnections IP1, . . . IPL, e.g. pins, via L-communication lines CL1, .. . CLL. The number of channels of the output stage would typicallycorrespond to the number of channels N of the pulse modulator circuitryPMC. It should in this context be stressed that the invention may applyeven with only one communication line as the sole communication linefrom the modulator to the output stage, although two lines have beenshown in the drawing.

The switched output stage may be arranged in one chip or in a multi-chiparrangement as indicated by the dotted lines.

The multi-channel switched output stage SWOS receives the output pulsemodulation representations OPMr, and a pulse signal splitter PSS decodes(splits) the signal into N channels of reestablished pulse modulatedsignals RMS. The N channels of reestablished pulse modulationrepresentations are then fed to switched output stages SOS and output bymeans of N-output channels OC1, OCN.

In the illustrated embodiments, each of the outputs are fed todemodulators and subsequently fed to loudspeakers LS.

According to a preferred embodiment of the invention, the abovedescribed pulse modulator circuit PMC may advantageously comprise apulse modulator chip comprising a number of output connectionspreferably constituted by output pin(s).

FIG. 3A-3C illustrate a few out of several different principletopologies of PWM-amplifier system which may find use in a multi-channelsystem of the invention,

FIG. 3A illustrates an embodiment of a pulse width modulator system PWMSof an embodiment of the invention. It comprises a modulator input MIreceiving an input signal IS. The input signal is preferably the utilitysignal to be pulse width modulated. An amplitude distribution filter ADFprocesses the input signal IS in order to adapt the input signalamplitude distribution to achieve the best performance of subsequentstages. The amplitude distribution filter ADF establishes an outputsignal OS, also referred to as intermediate output signal, which is fedto a pulse width modulator PMOD. The pulse width modulator PMODestablishes a pulse width modulated representation of the output signal,and outputs it via a modulator output MO as a modulator output signalMOS. It is noted that the illustrated embodiment is merely an example,and that several other pulse width modulator systems are suitable foruse with the present invention. In a preferred alternative embodiment,the amplitude distribution filter ADF is, e.g., integrated into thepulse width modulator PMOD in such a way that it would render a simpleillustration unclear with respect to the present invention. A preferredembodiment is disclosed in co-pending application PCT/DK2004/000376,hereby incorporated by reference.

FIG. 3B illustrates a further embodiment of a pulse width modulatorsystem PWMS of the present invention, and a context for its use. Itcomprises all elements of FIG. 1A coupled as described above. Itfurthermore comprises an amplifier AMP receiving the modulator outputMOS. The amplifier is preferably of the power switch type, but may beany amplifier suited for amplifying a PWM-signal. The amplifier maycomprise any number of switches and couplings of these, in accordancewith the type of PWM-modulation scheme used by the PWM-modulator PMOD.The amplifier outputs a modulator system output signal MSOS via anamplifier output AMPO. The modulator system output signal MSOS being theoutput of the pulse width modulator system PWMS of the presentembodiment is preferably demodulated by means of a demodulator DEM,typically a low-loss, low-pass filter, and is fed to a loudspeaker LS.According to the particular PWM-modulation scheme used, the amplifier,demodulator and loudspeaker may be coupled in any way suitable. Thisparticularly applies for systems where the PWM-signal is distributedover two or more simultaneous signal parts, e.g. as typically used forthree level PWM-signals.

FIG. 3C illustrates a further embodiment of a pulse width modulatorsystem PWMS of the present invention, and in particular illustrates anexample of an embodiment of the pulse width modulator PMOD. Theillustrated system comprises a PWM-amplifier/audio system for use with adiscrete time input signal, e.g. a pulse code modulated (PCM) signal.

Like the embodiment of FIG. 1B the present embodiment comprises amodulator system input MI feeding an input signal IS to an amplitudedistribution filter ADF. The intermediate output signal OS of theamplitude distribution filter ADF is fed to the pulse width modulatorPMOD.

The modulator output MOS of the pulse width modulator PMOD, i.e. a pulsewidth modulated signal, is amplified by means of an amplifier AMP asdescribed above and rendered into sound by means of a demodulator DEMand a loudspeaker setup LS as also described above.

FIG. 3C further illustrates an embodiment of a pulse width modulatorPMOD. It comprises an upsampling block 11 basically transforming theintermediate output signal OS from one sampling frequency representationinto an N times higher sampling representation.

The upsampled signal is then fed to an intersection-computing block 12adapted for determination of intersections with a parallel referencesignal representation 16 provided by a reference signal generator 15.The intersections may e.g. be established in the block 12 according tothe principles disclosed in PCT/DK03/00334 hereby incorporated byreference, or in PCT/DK2004/000361 hereby incorporated by reference. Aconsecutive noise shaping and quantizing block 13 feeds the establishedintersections to a pulse generator 14 which establishes the modulatoroutput signal MOS, i.e. a pulse width modulated signal. In analternative embodiment the amplitude distribution filter ADF, or partsof it, may be integrated with the noise shaping and quantizing block 13of the pulse width modulator PMOD.

It is noted that the above-described embodiment of a pulse widthmodulator PMOD is only one of several possible embodiments suitable foruse with the present invention. Also several different kinds of pulsewidth modulation and encoding schemes may be used for establishing thepulse width modulated signal MOS. This signal may thus perfectly bedistributed over several sub-signals, e.g. when differential PWM-signalsare established. In such cases also the amplifier AMP may compriseseveral sub-amplifiers, typically power switches, and the demodulatorDEM may comprise several demodulators. Also the loudspeaker setup maycomprise several signal inputs.

An example of a further pulse width modulator PMOD embodiment that maybe used with the present invention is disclosed in PCT/DK03/00475,hereby incorporated by reference.

A further example of a pulse width modulator PMOD embodiment that may beused with the present invention is disclosed in EP 1 178 388 A1, herebyincorporated by reference.

It is noted that the above-mentioned embodiment examples are notexhaustive, and that the present invention may be used in any contextfor any application and that the illustrations in FIGS. 3A, 3B and 3Care only examples for establishing a concept and context for thefollowing detailed description.

It is noted, with reference to the below explanation of FIG. 4A that amodification of the FIGS. 3B and 3C has to be made in order to apply theprinciples of the invention in a multi-channel system. Thus, when usinge.g. N of the illustrated systems in parallel in a multi-channelamplifier setup, modulator output signals MOS of the pulse widthmodulator system of e.g. FIG. 3B or FIG. 3C are merged or combinedwithin the modulator chip to e.g. two communication lines and interfacedto the switched output stage, e.g. a chip.

FIG. 4A illustrates a principle embodiment of the invention.

An example of an application where dynamically positioned problematicamplitude ranges may be advantageously utilized is given in FIG. 4A.

More details about the specific embodiment are given in the co-pendingPCT/DK2004/000376, hereby included by reference. This applicationbasically addresses the need for counteracting undesired side effectsdue to limited slew rate when outputting narrow pulses, resulting in adistortion of the pulse established by the output stage. Suchcounteracting, i.e. the method and means described in detail inPCT/DK2004/000376, may be applied advantageously together with theprinciples of the present invention in a multi-channel output stage as amodification of the signal fed to the switching stage may advantageouslyby applied to minimize cross-talk in the output stage by minimizing orremoving switching at the same time. Such compensation requires a mutualcontrol or interaction, as the switching or the intended switching ofone channel may result in a modified switching of another channel.

It comprises an embodiment of a multi-channel PWM modulator system MCSembodied in a pulse modulator chip PMC. Such a system may e.g. be usedfor pulse width modulating several audio channels, e.g. 6 channels, andmay advantageously be implemented in a single integrated circuit. One ofseveral issues to consider when implementing a system in an integratedcircuit is the use of output connectors, here output pins, as the numberof these significantly impacts the cost of the integrated circuit, i.e.production and materials. A possible solution to this problem is tocombine the multiple audio channels into a fewer number of physicalconductors. When e.g. the system comprises 6 audio channels it may bepossible by means of a proper multiplexing algorithm, compressionalgorithm, etc., to combine the information of these into e.g. 2 or 4physical wires. In FIG. 4 is shown two signals entering themulti-channel PWM modulator system MCS. These signals may each requiremore than one physical connector, but use together preferably less than6 connectors. Within the multi-channel system MCS the combined channelssignal is split into a signal for each of the 6 individual channels by asignal splitter 121. Alternatively, each of the 6 channels may enter themulti-channel system MCS by its own physical connector. Each of the 6channels are provided to a pulse width modulating system PWMS1, PWMS2, .. . , PWMS6 as input signals, whereof due to clarity in the drawing onlya reference IS1 is given for the first channel. The modulator outputsignals MOS1, etc., which are pulse width modulated representations forthe input signal IS1, etc. are again combined into less than 6physically wired signals by means of a signal combiner 123.

FIG. 4A further comprises a signal splitter 124 for dividing thecombined modulator output signal into a reestablished pulse modulationsignal RMS1, . . . , RMS6 for each channel outside the integratedcircuit comprising the multi-channel pulse width modulator system MCS.The signal splitter 124 forms part of a pulse signal splitter PSS asdescribed and explained with reference to FIG. 2. Each of these pulsewidth modulated output channels may then be fed to, e.g., separateamplifiers AMP1, . . . , AMP6, preferably switch-mode amplifiers.Alternatively the combined modulator output signal may be fed directlyto each of the subsequent, e.g. amplifiers, by bypassing the signalsplitter 124. The subsequent stage, e.g. amplifier, should then beadapted to retrieve from the combined signal only the relevant channel.

In order to most optimally combine multiple pulse width modulatedsignals MOS1, etc., into a fewer physical signals by means of signalcombiner 123, it may be beneficial to assume that none of thePWM-signals comprise concurrent pulse flanks. As the input signalamplitudes determine the pulse widths, and thus the flanks of thepulses, non-concurrent pulse flanks may be ensured by ensuring that apulse width modulator PMOD of one pulse width modulator system PWMS1, .. . , PWM6 never receives the same intermediate output signal OSamplitude at the same time as the modulator of another system PWMS1, . .. , PWMS6, as this would probably cause concurrent pulse flanks to beestablished.

A further reason for desiring non-concurrent pulse flanks is theprobability of establishing cross-talk when, e.g., the amplifiers AMP1,. . . , AMP6 are operated from the same power supply. By ensuring thatthe switches in different amplifiers are never required to switchsimultaneously, the problem of cross-talk may be reduced.

Guaranteeing or at least increasing the probability of non-concurrentflanks in a multi-channel system, e.g. a stereo system or a 5.1 system,is thus desired, and one way in which this may be ensured is, within theexample embodiment of FIG. 4A, by dynamically adapting the problematicamplitude ranges of some of the pulse width modulator systems PWMS1, . .. , PWMS6 according to the intermediate output signal amplitudes ofother pulse width modulator systems PWMS1, . . . , PWMS6.

Such dynamically adapting of the problematic amplitude ranges may e.g.be performed by a pulse amplitude distribution manager 122 connectedwith each pulse width modulator system PWMS1, . . . , PWMS6 by means oftwo-way external control signals ECS1, etc. Thereby the pulse amplitudedistribution manager 122 may continuously obtain information of thecurrently processed input values or intermediate output values, andadaptively establish control information accordingly. Within each pulsewidth modulator system PWMS1, . . . , PWMS6 an amplitude distributionfilter ADF as mentioned above, or other suitable means, may communicatewith the pulse amplitude distribution manager 122 and on the basis ofthe relevant input signal IS1 and external control signal ECS1 causeestablishment of non-concurrent flanks.

The signal combiner 123 and the pulse amplitude distribution manager 122thus forms a pulse signal combiner PSC as described and explained withreference to FIG. 2.

Evidently, the invention may be applied in several other technicalconcepts than the above-described.

FIG. 4B illustrates an alternative embodiment of an application asdescribed regarding FIG. 4A. FIG. 4B also comprises a multi-channelpulse modulator system MCS as described above. The multi-channel pulsemodulator system also comprises a pulse signal combiner PSC comprising apulse amplitude distribution manager 122 and a signal combiner 123. Thesignal combiner 123 of FIG. 4B establishes a data signal 202 and achannel code signal 203 on the basis of the, e.g., six modulator outputsignals MOS1, . . . , MOS6. FIG. 4B further comprises a pulse signalsplitter PSS, which comprises a decoder 201 and parts of the outputstages AMP1, . . . , AMP6. The data signal 202 comprises a compressedrepresentation of the switching times for all channels, and ispreferably transferred by means of a single wire. The data signal 202 isconnected to all output stages AMP1, . . . , AMP6, which preferablycomprise latches, e.g. flip-flops, in order to be able to read the datasignal 202. The channel code signal 203 may, e.g., be a 3-bit signaltransferred over 3 wires, and thus able to address up to 8 channels bybinary representation. For every switching time comprised by the datasignal 202, the channel code signal 203 preferably comprises a pointerto the channel to which the switching time correspond. The decoder 201decodes the channel code signal 203 and is on this basis able to enablethe latch of the corresponding output stage.

FIG. 5A comprises a timing diagram illustrating possible signal contentsin order to clarify how the above-described mechanism may work. FIG. 5Acomprises the modulator output signal MOS1, MOS2, MOS3, of three of thechannels of FIG. 4B. Each signal comprises a PWM pulse, but with nosimultaneous edges. FIG. 5A further comprises the data signal 202, i.e.a compressed representation of the modulator output signals MOS1, MOS2,MOS3. Each pulse in the data signal 202 represents an edge, eitherrising or falling. The width of each pulse in the data signal 202 ispreferably as short as possible while still wide enough to be detectedby the latches of the output stages. As there are no simultaneous edges,there is no problem in combining the edges of the modulator outputsignals into a single data signal. In order for the output stages toknow which of the data signal pulses correspond to which channels, achannel code signal 203 is establish in correlation with the data signal202. A possible channel code signal 203 is shown in FIG. 5A. In a periodfrom a little before each pulse of the data signal 202 it is set to abinary value representing the respective channel. Via the decoder 201this causes the latch of the output stage corresponding to that channelto be enabled in time for reading the pulse of the data signal 202.

In FIG. 4B the data signal 202 is shown as a bi-directional signal. Inaddition to the working mode describe above, the data signal 202 mayalso be used for transmitting feedback from the output stage AMP1, . . ., AMP6 to the pulse modulator circuit PMC. Such feedback may, e.g.,comprise the actual switch times established by the output stages. Asthe output stages typically comprise not only a fixed delay but alsovarying delays, e.g. dependent on the input signal, such information maybe used for further pre-correction or compensation within the pulsemodulator circuit PMC. Other possible feedback may comprise informationabout the state of the output stages, e.g. if an output stage is in anillegal state, or otherwise malfunctioning, or information aboutvariations in the power supply voltage provided to switching outputstages. As the output stage delay is typically longer than the necessarywidth of the data signal pulses, the feedback may be established on thedata signal wire during the period between the end of a switch timerepresenting pulse and until the next switch time representing pulse.Such a data signal 202 comprising feedback is illustrated in FIG. 5B.When the signal combiner 123 has established a switch time representingpulse for some channel it doesn't use the data signal wire until thenext switch time representing pulse has to be established. In theintervening time the output stage may use the wire for feedbackpurposes. The available feedback time slot may be pre-defined, or, e.g.,controlled by the channel code signal, a further clock signal, or anyother suitable signal. In case of using the feedback feature, the pulsemodulator circuit PMC should evidently comprise a circuitry forreceiving, interpreting and using the feedback. This may, e.g., beimplemented by the pulse amplitude distribution manager 122. Forfeedback interpretation purposes the channel code 203 or a separatecontrol signal may further be provided to the pulse modulator circuitPMC.

The data signal 202 may comprise adjusted switch time representations orreference switch time representations. In the first case the pulsemodulator circuit PMC comprises correcting and compensation logic forattempting to correct the errors in the output stages. In the lattercase the pulse modulator circuit PMC merely transmits the correctreference switch time representations, and lets the output stagescorrect or compensate their own errors. In such case the output stagesmay comprise local, analog feedback. Thereby, e.g., power supply errorsor variations may be compensated. In a further embodiment a combinationis applied, where local, analog feedback in the output stages establisherror information, which may be fed back to the pulse modulator circuitPMC by means of the data signal 202 or a separate signal.

FIG. 6 illustrates a detailed view of an embodiment of the connectionbetween a pulse signal combiner PSC and a pulse signal splitter PSSaccording to the present invention. The pulse signal combiner PSCcomprises N inputs, MOS1, . . . , MOS6, also referred to as output pulsemodulation representations OPMr. In the present embodiment N is six.Each input represents an input channel of a pulse modulator system PMC,e.g. audio channels. The pulse signal combiner PSC establishes anM-channel communication signal 202, 203, which is transmitted to thepulse signal splitter PSS by means of L output connections. In theembodiment of FIG. 6 M is two as it, e.g., comprises a data signal 202and a channel code 203. As the channel code in the present embodimentuses 3 wires, L is 4 in the present embodiment. The pulse signalsplitter PSS establishes a number of output channels RMS1, . . . , RMS6,preferably corresponding to the N input channels.

It is noted that the embodiment of FIG. 6 is an example, and that anyvalues of N, M and L are within the present invention, as long as N isgreater than L, i.e. the communication between the pulse signal combinerPSC and pulse signal splitter PSS uses less connections from the pulsemodulator circuit PMC than the number of channel processed by themulti-channel pulse modulator system MCS.

Hence connections between the signal combiner and signal splitter may beuni- or bi-directional, may be a multilevel signals, may comprise anynumber of connections less than N, including 1 connection, may utilizeany communication protocol and data transfer technology, etc. Thus, inan alternative embodiment only one wire connects the pulse modulatorcircuit PMC and the pulse signal splitter PSS, that wire comprising amultilevel signal where, e.g., the signal level is used for transmittingthe channel code information.

1. A multi-channel pulse modulator system comprising a pulse modulatorcircuit, wherein said pulse modulator circuit comprises an N-channelpulse width modulator for modulating an N-channel input signal, whereinmodulator output is multiplexed and output from the pulse modulatorcircuit by means of L output connections of the pulse modulator circuitand where L is less than the number of modulator channels N.
 2. Amulti-channel pulse modulator system according to claim 1, wherein saidmulti-channel pulse modulator system further comprises a switched outputstage, wherein said pulse modulator circuit comprises an N-channel pulsewidth modulator, wherein the modulator output is interfaced from thepulse modulator circuit to the switching output stage by means of Loutput connections, of the modulator circuit and where L is less thanthe number of modulator channels N.
 3. A multi-channel pulse modulatorsystem according to claim 1, wherein the L output connections outputs anM-channel signal where M is less than N, wherein said M-channel signalis established by a pulse signal combiner, wherein said pulse signalcombiner combines at least one of said M-channel signals into anon-coincident pulse modulated signal representing at least a subset ofan N-channel pulse modulated signal established by said N-channel pulsewidth modulator.
 4. A multi-channel pulse modulator system according toclaim 2, wherein the number of output channels of the switching outputstage is N.
 5. A multi-channel pulse modulator system according to claim3, wherein said pulse signal combiner combines said N-channel pulsemodulated signal by an initial establishment of said N-channel pulsesignal of non-coincident pulses and whereby said non-coincident pulsessubsequently are combined into said M-channel signal.
 6. A multi-channelpulse modulator system according to claim 3, whereby said M-channeloutput comprises a sequence of analog pulses, and whereby said sequenceof analog pulses defines the pulses of an N-channel pulse modulatedsignal.
 7. A multi-channel pulse modulator system according to claim 1,wherein said pulse modulator circuit comprises a pulse modulator chip.8. A multi-channel pulse modulator system according to claim 1, whereinsaid L connections comprises L output pins.
 9. A multi-channel pulsemodulator system according to claim 2, wherein said switched outputstage is comprised in one single chip.
 10. A multi-channel pulsemodulator system according to claim 2, wherein said switched outputstage is distributed in two or more chips.
 11. A multi-channel pulsemodulator system according to claim 1, wherein said pulse modulation isa two-level modulation, a three-level modulation or a higher-levelmodulation.
 12. A multi-channel pulse modulator system according toclaim 1, wherein said multi-channel pulse modulator system comprises apulse width modulation system comprising a multi-channel pulse widthmodulator comprised in said pulse modulator circuit.
 13. A multi-channelpulse modulator system according to claim 1, wherein said pulsemodulator system is an audio converter
 14. A multi-channel pulsemodulator system according to claim 2, wherein at least one of saidL-output connections facilitate a bi-directional communication betweenthe modulation circuit and said output stage.
 15. A multi-channel pulsemodulator system according to claim 2, wherein said pulse modulatorcircuit comprises at least one connection dedicated for receipt ofinformation from the state of the output stage.
 16. A multi-channelpulse modulator system according to claim 2, wherein said output stagecomprises a pulse signal splitter.
 17. A multi-channel pulse modulatorsystem according to claim 16, wherein said pulse signal splittercorrects modifications applied in the pulse signal combiner.
 18. Amulti-channel pulse modulator system according to claim 1, whereby thenumber L of output connections is one.
 19. A multi-channel pulsemodulator system according to claim 1, whereby the number L of outputconnections is two.
 20. A multi-channel pulse modulator system accordingto claim 3, whereby at least one of said M-channels are bidirectional.21. A multi-channel pulse modulator system according to claim 3, wherebyat least a subset of said M-channels are directed from the pulsemodulator circuit.
 22. A multi-channel pulse modulator system accordingto claim 21, whereby at least a further subset of said M-channels aredirected to the pulse modulator circuit.
 23. A multi-channel pulsemodulator system according to claim 3, wherein said M-channel signal isconverted into an N-channel signal and distributed to N-channels of anoutput stage as pulse modulated signals.
 24. A multi-channel pulsemodulator system according claim 23, wherein said N-channel signaldistributed to said output stage corresponds to an N-channel signalestablished by an N-channel pulse width modulator of said pulsemodulator circuit.
 25. Method of converting an N-channel pulse widthmodulated signal established from an N-channel input signal into anM-channel signal, where M is less than N, said method comprising:modifying at least one of said M-channel signals into a non-coincidentpulse modulated signal representing at least a subset of said N-channelpulse width modulated signal and where said subset of said N-channelpulse width modulated signal comprises at least two channels.
 26. Methodof converting an N-channel pulse width modulated signal into anM-channel signal according to claim 25, whereby said converting of saidN-channel pulse width modulated signal comprises an initialestablishment of said N-channel pulse width modulated signal ofnon-coincident pulses and whereby said non-coincident pulsessubsequently are combined into said M-channel signals.